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Home / Codes / P0689
DTC code page

P0689: ECM/PCM Power Relay Sense Circuit Low

Quick answer: The PCM saw relay-output feedback lower than expected on the sense circuit.

Drivers also search this fault as PCM power relay sense low, ECM relay feedback low, PCM relay output low.

Severity: high Family: powertrain Related paths: 15
Meaning

What P0689 usually means

P0689 means the relay-output feedback exists, but it is lower than the PCM expects. That often points to voltage drop through relay contacts, weak battery supply, corroded fuse-box connections, or a sense circuit being pulled down enough to look unreliable. It is less about total loss and more about an underfed power path.

Fast triage

Start here before chasing parts

  • Scan first: save freeze-frame and pending codes before clearing anything.
  • Confirm the complaint: compare the stored code with current drivability symptoms.
  • Use context: trims, live data, and related codes usually narrow the fault faster than guesswork.
  • Work simplest to hardest: leaks, connectors, maintenance items, and known patterns before expensive components.
Initial checks

What to check first

  • Measure actual voltage at the PCM feed during crank, not just battery voltage at rest.
  • Inspect for heat-discolored relay or fuse terminals that add resistance under load.
  • Look for companion low-voltage or charging complaints because they often explain the story.
Driving risk

Can you keep driving?

P0689 can produce intermittent reduced-power, restart, or stall behavior if PCM feed voltage keeps sagging. It is usually unsafe to ignore once symptoms are active.

High urgency: If symptoms are active, reduce driving and diagnose quickly before secondary damage builds.
Likely causes

Common causes behind this code

  • Weak battery or cranking voltage sag
  • Voltage drop across worn relay contacts
  • Corroded power or ground connection in the PCM feed path
  • Sense wire with high resistance or partial short to ground
  • Fuse-box terminal heating causing under-voltage on the output side

Cause phrases often tied to this code: voltage drop, relay contacts, sense circuit low, weak battery, corrosion.

Diagnostic order

Suggested workflow

  1. Record freeze-frame and see whether the code sets mostly during crank, hot restart, or while driving.
  2. Load-test the battery and verify charging-system health.
  3. Measure voltage drop across the relay contacts and fuse-box feed path.
  4. Inspect the sense circuit for high resistance, corrosion, or partial grounding.
  5. Confirm stable PCM voltage after the repair under the same load that used to trigger the code.
Avoid guesswork

Common mistakes

  • Replacing the relay without proving where the voltage drop actually lives.
  • Treating P0689 like a pure sensor problem instead of a power-distribution problem.
  • Ignoring hot-soak behavior that reveals resistance faults better than cold tests do.
Repair path

Practical fix guidance

  • Fix the proven under-voltage source in the relay-output or sense path: relay, terminal, fuse-box, battery, or wiring.
  • Retest under hot and cranking load because many low-sense faults only appear under stress.
  • If charging codes remain, continue the diagnosis instead of assuming the relay repair solved everything.
Vehicle context

Affected brands in this MVP

Brand hubs help broaden internal linking now and can evolve into make-specific diagnostic notes later.

Aliases and common searches

English phrases tied to P0689

Useful when the driver knows the wording but not the exact DTC yet.

  • PCM power relay sense low
  • ECM relay feedback low
  • PCM relay output low
Related search intent

Queries this page can answer naturally

  • P0689 code meaning
  • what does P0689 mean
  • PCM power relay sense circuit low
FAQ

Quick questions about P0689

How is P0689 different from P0688?

P0688 points to missing or open relay-output feedback, while P0689 points to feedback that is present but too low.

Can bad relay contacts cause P0689?

Yes. Burned contacts can pass some voltage but still drop enough under load to trigger a low-sense fault.

Why does P0689 often show up during hot restart?

Resistance faults in relays, fuse boxes, and terminals often get worse as heat rises.